The present invention relates to an antifriction bearing unit and a water pump.
Conventionally used in water pumps is an antifriction bearing unit which comprises a solid rotating shaft having a large-diameter shaft portion serving as an inner ring and a small-diameter shaft portion integral with the shaft portion, an outer ring fitted around the large-diameter shaft portion and fixed to a housing, and rolling members arranged between the large-diameter shaft portion and the outer ring. A pulley is mounted on the end (outer end) of the shaft providing the large-diameter portion, and an impeller on the other shaft end (inner end) having the small-diameter portion.
With the conventional antifriction bearing unit, the rotating shaft is solid and comprises a large-diameter portion and a small-diameter portion which are formed integrally, and therefore has the problem of being very heavy when elongated in axial length.
Further difficulties are encountered in making the large-diameter portion and the small-diameter portion integrally as by lathe turning and grinding, entailing a poor material yield and a higher cost. Since the large-and small-diameter shaft portions are made in the form of an integral piece, the small-diameter shaft portion which need not be of a rolling fatigue property must be prepared from the same bearing steel material as the large-diameter portion, and when the corrosion inhibition treatment for the small-diameter portion is to be performed also for the large-diameter portion, it becomes necessary to mask the raceway grooved portions for the treatment, hence the problem of additional difficulties and an increased cost.
Although it has been proposed to provide a hollow integral rotating shaft comprising a large-diameter portion and a small-diameter portion by making races by plastic working, there still remains the problem that preparing the entire shaft from a bearing steel results in an increased cost and difficult working even if the shaft is a hollow integral piece (see JP-A No. 2000-65070).
Additionally, the antifriction bearing unit usable in water pumps requires seal devices for assuring the bearing portion of reliable rotational performance.
However, when the antifriction bearing unit has incorporated therein a seal device comprising a metal slinger fixed to the rotating shaft by a press fit and a rubber seal member fixed in a groove formed in the outer ring as conventionally practiced, not only the number of parts corresponding to the slinger can not be reduced, but it is also impossible to reduce the number of management items for the production of the antifriction bearing unit, such as inspecting or monitoring the press-fit dimensions and pressing load involved in installing the slinger by a press fit, hence the problem of factors preventing improvements in productivity.